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Carbon nanotube antennas intensify solar energy

Scientists in the US have found a way of concentrating solar energy in a way they claim could make photovoltaic (PV) cells 100 times more powerful.

A team at the Massachusetts Institute of Technology (MIT) has developed antennas made from millions of carbon nanotubes that can capture and focus energy from photons.

This could allow the creation of smaller and more powerful arrays that effectively funnel light from the surrounding area into solar cells.

This filament containing about 30 million carbon nanotubes absorbs energy from the sun as photons and then re-emits photons of lower energy, creating the fluorescence seen here. The red regions indicate highest energy intensity, and green and blue are low

This filament containing about 30 million carbon nanotubes absorbs energy from the sun as photons and then re-emits photons of lower energy, creating the fluorescence seen here. The red regions indicate highest energy intensity; green and blue are lower intensity. Image: Geraldine Paulus

The research, described in the latest edition of the journal Nature Materials, could also have uses in other applications that require light to be concentrated, such as night-vision goggles or telescopes.

When photons hit the nanotubes at the surface of an antenna, their energy travels to the nanotubes at the centre via excitons. These comprise an electron that has been excited to a higher energy level and the hole in the atom it leaves behind.

Because excited electrons can exist at different energy levels, excitons ‘can migrate to adjacent nanotubes if the energy levels are lower, and you can use this principle to allow them to collect at a central, core nanotube filament,’ the project’s lead researcher, Prof Michael Strano, told The Engineer.

‘In this way, they become concentrated in space to where you might have an optoelectronic device such as a PV cell, which would turn the excitons into electrons and holes for power applications.’

Recent developments allowing scientists to separate nanotubes with different properties, along with their falling cost, have made the work possible. The team now plans to build a solar device, which may take another one or two years.

‘You could envision that such a concentrator might boost power production of a much smaller solar cell by a factor of 100,’ said Strano.

Because the antennas funnel light from a large to a small area, the resulting solar cells could be much smaller and spaced further apart than existing designs.

‘The advantages here range from easier manufacturing, defect resistance and fault tolerance, to flexibility and maybe lower cost,’ added Strano.

The antennas measure around 10 micrometres (millionths of a metre) long and four micrometres thick, and would likely form a coating that could be painted or sprayed onto a PV cell, or could be built into the device with the PV material integrated around them.

The team is working on generating more than one exciton per photon and on minimising the energy lost as excitons flow through the antennas. They currently lose about 13 per cent of the energy they absorb, but this could be reduced to as little as one per cent.

Strano was also involved in the recent invention of a photoelectrochemcial cell that can repair itself when damaged by the sun.


Readers' comments (4)

  • It seems that it is MUCH cheaper just to use an inexpensive Fresnel Lens to concentrate the light versus carbon nanotubes!! Typically there are optics the direct concentrated light to the solar cell like Sol Focus (www.solfocus.com) or Amonix (www.Amonix.com) or in the case of a Rainbow Concentrator will separate and concentrate the light like Sol Solution (www.sol-solution.net).

    Using carbon nanotubes in solar energy is so ridiculously expensive that it is laughable.

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  • This is the right route because I was working in solar energy for more than 30 years and the low concentration was my problem.

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  • The article does say that using solar concentration allows use of smaller cells SPACED FURTHER APART. I assume that overall the power density is not increased - it just needs less silicon.

    There might be a wee problem with heat dissipation though.......

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  • Indeed, I am failing to see the benefit here. A 1m*1m area will still produce the same amount of energy, you just need a 1m*1m nano tube covered area which feed to a smaller piece of silicon, than a 1m*1m silicon cell.
    So what's the advantage, we're not in danger of running out of sand?
    Sure the solar cell can be smaller but the nano tubes are going to be expensive and complex.
    I see no practical use for this.

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